In order for different units in a local environment to be able to exchange information, there are at present a number of different technologies that make possible short-range communication. One example of such short-range communication is radio communication according to the Bluetooth® standard or the WLAN standard.
Units adapted to such short-range communication include such portable user units as mobile telephones, portable computers and PDAs, as well as the pen-shaped sensor device described in the Applicant's Patent Applications WO 01/16691 and WO 01/48685, which are herewith incorporated by reference.
These user units can be operated for direct connection, via short-range communication, to a server unit with a particular attribute/service. In order for a user unit to be able to connect to the particular server unit, it needs, however, to know the address thereof for short-range communication.
The user unit can only store a limited number of addresses, which in general makes impossible the storage of addresses of all the server units. Since it is desirable to be able to use the user unit in different local environments, such as in different towns or countries, it is in general also impossible to permanently store in advance a relevant subset of the addresses of all server units in a memory of the user unit.
A conceivable way of tackling this problem would instead be to utilize a linear search method, in which the user unit is caused to implement a series of connection attempts to every possible address. Such a method, however, will be undesirably time-consuming.
Another alternative solution could be that, at a request from a user unit, each server unit is able to implement a search within, or forward the request to, other server units in its vicinity for a desired attribute/service. However, with short-range communication, the range is in general insufficient for such a distributed search, that is the server units are located at a distance that makes it impossible for them to communicate with each other.
Alternatively, the user unit, or a server unit contacted by the user unit, could via a communication network implement a look-up in a central database holding associations between attributes/services and addresses for short-range communication. Such a solution can be hampered by slow connection to the central database. In addition, the central database must be constructed and maintained, which is costly.
An additional possible solution, in the following called the enquiry method, could be to let the user unit intermittently transmit an enquiry signal that causes other units in the vicinity to return their address, whereby the user unit can build up an internal database of addresses of units that are within its radius of communication. Such a technique can, however, be time-consuming if there are many units in the vicinity, particularly if it is desirable for connection to be carried out to one specific unit. Another problem with this method is that it does not always lead to the correct unit being found, due to an incorrect unit being selected or due to all units within reach not being available to answer enquiries. For instance, the Bluetooth standard allows only that a limited number of units communicate with each other, within a so-called pico-network, that is created when several units are in the same local environment.
Another possible method for specifying an address for communication is to enter the address of the specific unit manually. This method is, even more than the method above, associated with slow entering and sources of error, such as incorrect entry by the user. In addition, it is necessary for a user-interface to be available in order for the entry to be carried out.